asp.net mvc - Is it possible to create a generic @helper method with Razor?

Question

I am trying to write a helper in Razor that looks like the following:

@helper DoSomething<T, U>(Expression<Func<T, U>> expr) where T : class

Unfortunately, the parser thinks that <T is the beginning of an HTML element and I end up with a syntax error. Is it possible to create a helper with Razor that is a generic method? If so, what is the syntax?

Answer 1

This is possible to achieve inside a helper file with the @functions syntax but if you want the razor-style readability you are referring to you will also need to call a regular helper to do the HTML fit and finish.

Note that functions in a Helper file are static so you would still need to pass in the HtmlHelper instance from the page if you were intending to use its methods.

e.g. ViewsMyView.cshtml:

@MyHelper.DoSomething(Html, m=>m.Property1)
@MyHelper.DoSomething(Html, m=>m.Property2)
@MyHelper.DoSomething(Html, m=>m.Property3)

App_CodeMyHelper.cshtml:

@using System.Web.Mvc;
@using System.Web.Mvc.Html;
@using System.Linq.Expressions;
@functions
{
    public static HelperResult DoSomething<TModel, TItem>(HtmlHelper<TModel> html, Expression<Func<TModel, TItem>> expr)
    {
        return TheThingToDo(html.LabelFor(expr), html.EditorFor(expr), html.ValidationMessageFor(expr));
    }
}
@helper TheThingToDo(MvcHtmlString label, MvcHtmlString textbox, MvcHtmlString validationMessage)
{
    <p>
        @label
        <br />
        @textbox
        @validationMessage
    </p>
}
...